Sensing properties of undoped and Pt-doped SnO2 thin films deposited by chemical spray

In this work, undoped and platinum doped tin oxide (SnO2, SnO2:Pt) thin films were deposited on glass substrates by using the chemical spray pyrolysis technique. The starting solutions were prepared by dissolving tin chloride (SnO2·5H2O) in ethylic alcohol. For doping, platinum chloride (PtCl2) at atomic concentrations of 1 and 3 at% was used. Undoped-SnO2 thin films were deposited at different temperatures and times, varying between 300 and 500 °C in steps of 50 °C, and 1.5–7.5 min, respectively; whereas SnO2:Pt films were deposited in the range of 300–00 °C temperature interval at deposition times varying between 5 and 15 min. The film thicknesses and initial sheet resistances were in the range of 30–650 nm, and 150–5×104 Ω, respectively, depending on the deposition conditions. The crystalline structure of the samples was analyzed by X-ray diffraction (XRD). All the XRD patterns of the films showed a well-defined polycrystalline phase, fitting well with the SnO2 tetragonal type structure, and a strong dependence on the deposition conditions. The surface morphology was analyzed from Scanning electron microscopy. The effect of the deposition conditions, temperature and time, on the sensing properties of the films was studied in this work. The sensing properties of the SnO2 films in a carbon monoxide (CO) atmosphere, at different operation temperatures, were tested. According to the sensitivities values, doped films deposited in the 300–400 °C interval presented the best results. SnO2:Pt films deposited at 300 °C and a [Pt]/[Sn]=3 at% ratio showed the highest sensitivity, around 12, at an operation temperature of 300 °C.